/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* ans;

    bool dfs(TreeNode* root, TreeNode* p, TreeNode* q)
    {
        if (root == nullptr) return false;
        bool lson = dfs(root->left, p, q);
        bool rson = dfs(root->right, p, q);

        if ((lson && rson) || (root->val == p->val || root->val == q->val))
        {
            ans = root;
        }
        return lson || rson || (root->val == p->val || root->val == q->val);
    }


    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q)
    {
        dfs(root, p, q);
        return ans;
    }
};